Method for forming sealing film, and sealing film

ABSTRACT

A method for forming a sealing film, in which a buffer layer and a barrier layer whose density is higher than that of the buffer layer are alternately formed on a substrate, includes forming a first buffer layer on a surface of the substrate, forming a first barrier layer on a surface of the first buffer layer, and forming a second buffer layer on a surface of the first barrier layer. A ratio of a thickness of a portion of the first buffer layer in a thickness direction of the substrate relative to a thickness of a portion of the first buffer layer in an inclined direction that is inclined with respect to the thickness direction is closer to 1 than a ratio of a thickness of a portion of the second buffer layer in the thickness direction relative to a thickness of a portion of the second buffer layer in the inclined direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage of International ApplicationNo. PCT/JP2015/080475 filed on Oct. 29, 2015. This application claimspriority to Japanese Patent Application No. 2014-232014 filed with JapanPatent Office on Nov. 14, 2014. The entire disclosure of Japanese PatentApplication No. 2014-232014 is hereby incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates to a method for forming a sealing film ona substrate in order to prevent water from penetrating to the substrate,and to a sealing film that is formed on a substrate.

Background Information

Films with attached sealing films, formed for the purpose of preventingoxidation, moisture permeation, etc., have been used in recent years onthe surface of plastic films.

With a sealing film-attached film such as this, as discussed in JapaneseLaid-Open Patent Application Publication No. 2013-185207 (PatentLiterature 1), a buffer layer with good adhesion and a barrier layerwith good a barrier property with respect to the penetration of moistureare alternately laminated, thus forming on the base film a sealing filmthat is both flexible and provides a good barrier. In forming thissealing film, the buffer layer and barrier layer are mainly laminated byplasma CVD.

SUMMARY

With the above-mentioned thin-film formation device, however, there isthe risk that the barrier property of the sealing film thus formed wouldbe poor. More specifically, when a sealing film is formed by plasma CVD,if there is a stepped part such as an under-layer on the substrate 2 asshown in FIG. 5, buffer layers M1 and barrier layers M2 are formed so asto conform to this stepped part, but the thickness (the thickness B inFIG. 5) of the portion conforming to the stepped part (the portionformed in a direction that is inclined with respect to the thickness ofthe substrate 2) tends to be less than the thickness of the portionformed in the thickness direction of the substrate 2 (the thickness A inFIG. 5). In this case, there is the possibility that the buffer layer M1will not be formed properly on the surface of the stepped part of thesubstrate 2, and since the barrier layer that is subsequently formedwill not adhere well to this portion that is not formed properly, aproblem is that the sealing film ends up having extremely poor barrierproperties.

The present invention is conceived in light of the above problem, and itis an object thereof to provide a method for forming a sealing film withwhich a sealing film having a good barrier property can be formedstably.

To solve the above problem, the sealing film formation method of thepresent invention is a method for forming a sealing film in which abuffer layer and a barrier layer whose density is higher than that ofthe buffer layer are alternately formed on a substrate, said methodcomprising a first buffer layer formation step of forming the bufferlayer on the surface of a substrate, a first barrier layer formationstep of forming the barrier layer on the surface of a first buffer layerthat is the buffer layer formed in the first buffer layer formationstep, and a second buffer layer formation step of forming the bufferlayer on the surface of a first barrier layer that is the barrier layerformed in the first barrier layer formation step, wherein the ratio ofthe thickness of the portion of the first buffer layer formed in thethickness direction of the substrate relative to the thickness of theportion formed in a direction that is inclined with respect to saidthickness direction is closer to 1 than the ratio of the thickness ofthe portion of the second buffer layer, which is the buffer layer formedin the second buffer layer formation step, formed in the thicknessdirection relative to the thickness of the portion formed in a directionthat is inclined with respect to the thickness direction.

With the above-mentioned method for forming a sealing film, because theratio of the thickness of the portion of the first buffer layer formedin the thickness direction of the substrate relative to the thickness ofthe portion formed in a direction that is inclined with respect to saidthickness direction is closer to 1 than the ratio of the thickness ofthe portion of the second buffer layer, which is the buffer layer formedin the second buffer layer formation step, formed in the thicknessdirection relative to the thickness of the portion formed in a directionthat is inclined with respect to the thickness direction, the firstbuffer layer can be reliably formed even on a portion of the substratethat is not flat, so a sealing film with a good barrier property can beformed stably.

Also, it is preferable if the buffer layer and the barrier layer areformed by CVD, and the film formation pressure in the first buffer layerformation step is higher than the film formation pressure in the secondbuffer layer formation step.

As a result, the first buffer layer and the second buffer layer can beformed using the same formation chamber, and the sealing film pertainingto the present invention can be easily formed.

Also, to solve the above problem, the sealing film of the presentinvention is a sealing film formed by alternately forming a buffer layerand a barrier layer whose density is higher than that of the bufferlayer on a substrate, said sealing film comprising a first buffer layerthat is the buffer layer formed on the surface of the substrate, a firstbarrier layer that is the barrier layer formed on the surface of thefirst buffer layer, and a second buffer layer that is the buffer layerformed using the same raw material as the first buffer layer on thesurface of the first barrier layer, wherein the ratio of the thicknessof the portion of the first buffer layer formed in the thicknessdirection of the substrate relative to the thickness of the portionformed in a direction that is inclined with respect to said thicknessdirection is closer to 1 than the ratio of the thickness of the portionof the second buffer layer formed in the thickness direction relative tothe thickness of the portion formed in a direction that is inclined withrespect to the thickness direction.

With the above sealing film, because the ratio of the thickness of theportion of the first buffer layer formed in the thickness direction ofthe substrate relative to the thickness of the portion formed in adirection that is inclined with respect to said thickness direction iscloser to 1 than the ratio of the thickness of the portion of the secondbuffer layer formed in the thickness direction relative to the thicknessof the portion formed in a direction that is inclined with respect tothe thickness direction, the first buffer layer can be reliably formedeven on a portion of the substrate that is not flat, so a sealing filmwith a good barrier property can be formed stably.

With the method of the present invention for forming a sealing film, asealing film having a good barrier property can be formed stably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified view of a thin-film formation device forimplementing a sealing film formation method in an embodiment of thepresent invention, and is an oblique view;

FIG. 2 is a simplified view of a thin-film formation device forimplementing a sealing film formation method in an embodiment of thepresent invention, and is a front view;

FIG. 3 is a flowchart of the operations in the sealing film formationmethod in an embodiment of the present invention;

FIG. 4 is a simplified view of the structure of the sealing film of thepresent invention; and

FIG. 5 is a simplified view of the structure of a conventional sealingfilm.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment pertaining to the present invention will now be describedthrough reference to the drawings.

FIGS. 1 and 2 are simplified diagrams of a thin-film formation device 1for implementing the sealing film formation method in an embodiment ofthe present invention.

A thin-film formation device 1 is used to form a thin-film by performingsurface treatment on a substrate. For example, a sealing film whosepurpose is to prevent oxidation, moisture permeation, etc., is formed ona plastic film, and the product is used as a protective film for foods,a flexible solar cell, or the like. More specifically, in the case of aflexible solar cell, a solar cell made up of various electrode layers,opto-electrical conversion layers, and so forth is formed on a plasticfilm or other substrate, after which buffer layers and barrier layers(discussed below) are laminated over the solar cell with the thin-filmformation device 1 to form a sealing film. Consequently, moisture iseffectively prevented from penetrating to the solar cell, and a flexiblesolar cell with excellent oxidation resistance can be formed.

This thin-film formation device 1 has a conveyor roll 3 for playing outa band-shaped substrate 2, a conveyor roll 4 for winding up the suppliedsubstrate 2, a main roll 5 disposed between the conveyor roll 3 and theconveyor roll 4, a main roll chamber 6 that houses these rolls, and filmformation chambers 7 in which a thin-film is formed. The substrate 2played out from the conveyor roll 3 is conveyed along the outerperipheral face 51 of the main roll 5 while passing through the filmformation chambers 7, which forms a thin-film on the substrate 2, andthis is wound onto the conveyor roll 4.

The conveyor roll 3 and the conveyor roll 4 have a substantiallycircular-cylindrical core 31 and core 41. The substrate 2 is woundedonto the core 31 and the core 41, and these cores 31 and 41 arerotationally driven to play out or wind up the substrate 2. That is, thespeed at which the substrate 2 is played out or wound up can beincreased and decreased by controlling the rotation of the cores 31 and41 with a control device (not shown). More specifically, when the coreon the upstream side is rotated in a state in which the substrate 2 isunder tension from the downstream side, the substrate 2 is played out onthe downstream side, and the core on the upstream side is braked asneeded so that the substrate 2 will be played out at a constant speedwithout sagging. Also, the rotation of the core on the downstream sideis adjusted to prevent sagging of the played-out substrate 2, andconversely the substrate 2 can be wound up without being subjected tomore tension than necessary.

The substrate 2 here is a long, slender thin-film that extends in onedirection, and a strip with a flat shape having a thickness of 0.01 mmto 0.2 mm and a width of 5 mm to 1000 mm is used. There are noparticular restrictions on the material, but stainless steel, copper,and other such metal materials, or a plastic film or the like can beused to advantage.

The conveyor roll 3 and the conveyor roll 4 thus form a pair, one ofwhich plays out the substrate 2, and the other of which winds thesubstrate 2 at the same speed as the playout speed, which makes itpossible to convey the substrate 2 while keeping tension applied to thesubstrate 2 at a specific value. A mode is given above in which theconveyor roll 3 played out the substrate 2 and the conveyor roll 4 woundup the substrate 2, but the rotational direction of the conveyor roll 3and the conveyor roll 4 can be reversed so that the conveyor roll 4plays out the substrate 2 and the conveyor roll 3 winds up the substrate2, thus reversing the conveyance direction of the substrate 2.

The main roll 5 is a conveyor that holds the substrate 2 in a constantorientation during film formation, while conveying the substrate 2supplied from the conveyor roll on the upstream side to the conveyorroll on the downstream side. The main roll 5 is disposed between theconveyor roll 3 and the conveyor roll 4, and is in the form of asubstantially circular cylinder that is larger in diameter than the core31 and the core 41. The outer peripheral face 51 of the main roll 5 isformed as a curved surface with a constant radius of curvature in theperipheral direction, and its drive is controlled by a control device(not shown) according to the rotation of the core 31 and the core 41.The substrate 2 played out from the conveyor roll on the upstream sidecomes into contact with the outer peripheral face 51 of the main roll 5and is thereby conveyed in a state in which a specific tension isapplied. Specifically, the main roll 5 rotates according to the rotationof the conveyor roll 3 and the conveyor roll 4 in a state in which thesubstrate 2 is touching the outer peripheral face 51 of the main roll 5,the result being that the substrate 2 is conveyed from the conveyor rollon the upstream side to the conveyor roll on the downstream side in astate in which the entire substrate 2 is being tensioned and in anorientation in which the surface of the substrate 2 is opposite the filmformation chambers 7. Thus forming the film while the substrate 2 isconveyed in a taut state prevents the substrate 2 from fluttering duringfilm formation, which allows the thin-film laminated on the substrate 2to be formed in a more uniform thickness, and also prevents particlesfrom being generated by the fluttering of the substrate 2. Also, becausethe radius of curvature of the main roll 5 is set larger, film formationis carried out while the substrate 2 is supported in a state that iscloser to being flat, which prevents the substrate 2 from warping afterfilm formation.

The main roll chamber 6 is used to hold the main roll 5 and maintain theinside of the chamber at a constant pressure. In this embodiment, asshown in FIG. 1, the main roll chamber 6 is a casing formed in asubstantially pentagonal shape (roughly the shape of a baseball homeplate), with the main roll 5 accommodated in the center portion thereof.A vacuum pump 61 is connected to the main roll chamber 6, and thisvacuum pump 61 can be actuated to control the pressure inside the mainroll chamber 6. In this embodiment, the pressure is set to be lower thanthat in the film formation chambers 7. Also, in this embodiment, theconveyor roll 3 and the conveyor roll 4 are housed in the main rollchamber 6, but they may instead be provided outside the main rollchamber 6. Providing them inside the main roll chamber 6 as in thisembodiment protects the substrate 2 and the substrate 2 after filmformation (the film-attached substrate) against exposure to theatmosphere.

The film formation chambers 7 are used to form a thin-film on thesubstrate 2. In this embodiment, two film formation chambers 7 with thesame structure are provided. These film formation chambers 7 areprovided within the main roll chamber 6, and in the present inventionthe one closer to the conveyor roll 3 is called the first film formationchamber 7 a and the one closer to the conveyor roll 4 is called thesecond film formation chamber 7 b. When it is unnecessary to distinguishbetween the first film formation chamber 7 a and the second filmformation chamber 7 b, they are referred to collectively as the filmformation chambers 7.

The first film formation chamber 7 a and the second film formationchamber 7 b are formed by disposing partitions 62 on the outside of themain roll 5. More specifically, three substantially flat partitions 62are provided on the outside of the main roll 5, extending toward theouter peripheral face 51 of the main roll 5, thereby forming the twofilm formation chambers 7 that are formed by the outer peripheral face51 of the main roll 5, the partitions 62, and the walls of the main rollchamber 6, surround part of the film formation surface of the substrate2 on the main roll 5 (the face on the opposite side from the face thattouches the main roll), and form a closed space between themselves andpart of said film formation surface. Consequently, when the substrate 2is conveyed along the main roll 5 from the conveyor roll 3 to theconveyor roll 4, for example, the substrate 2 that passes the firstpartition 62 is conveyed into the first film formation chamber 7 a, andthen the substrate that passes the second partition 62 is conveyed intothe second film formation chamber 7 b, thereby successively formingthin-films on the substrate 2 in the first film formation chamber 7 aand the second film formation chamber 7 b.

This embodiment is configured such that a slight gap is provided betweenthe substrate 2 on the main roll 5 and the ends of the partitions 62 inorder to prevent damage to the substrate 2 due to interference betweenthe partitions 62 and the substrate 2. Therefore, the space formedbetween the film formation chambers 7 and the substrate 2 is not aclosed space in a strict sense, but for the purposes of this descriptionwe shall call it a closed space even though it is actually a space withthese slight gaps.

Vacuum pumps 71 a and 71 b are connected to the film formation chambers7, and the vacuum pumps 71 a and 71 b can be actuated to set theinterior of the first film formation chamber 7 a and the second filmformation chamber 7 b to a specific pressure. In this embodiment, theinside of the film formation chambers 7 is reduced to a specificpressure before the raw material gas is supplied.

Also, these film formation chambers 7 are provided with a film formationsource featuring plasma CVD, as a surface treatment of the substrate 2.Specifically, the film formation chambers 7 are provided withsubstantially U-shaped plasma electrodes 72 a and 72 b that areconnected to a high-frequency power supply (not shown) and are used forgenerating a plasma in the closed space within the film formationchambers 7, and these are connected to raw material gas pipes 73 a and73 b, which are raw material gas supply means. More specifically, thefirst film formation chamber 7 a is provided with the plasma electrode72 a, which is connected to a high-frequency power supply, and thesecond film formation chamber 7 b is provided with the plasma electrode72 b, which is connected to a high-frequency power supply. Also, thefirst film formation chamber 7 a is connected to raw material gas pipes73 a and an electrical discharge-use gas pipe (not shown), and thesecond film formation chamber 7 b is connected to raw material gas pipes73 b and an electrical discharge-use gas pipe (not shown). Consequently,a specific thin-film is formed on the substrate 2 passing through thefirst film formation chamber 7 a and the second film formation chamber 7b. That is, in a state in which raw material gas and discharge-use gashave been supplied into the film formation chambers 7, a high-frequencyvoltage is applied to the plasma electrodes 72 by a high-frequency powersupply, which generates a plasma in the discharge-use gas around theplasma electrodes 72. The raw material gas is decomposed by this plasma,reaches the substrate 2, and forms a specific thin-film on the substrate2. In this embodiment, in the first film formation chamber 7 a, HMDS(hexamethyldisilazane) gas, argon gas, and hydrogen gas are supplied asthe raw material gas to form a silicon component film (buffer layer),and in the second film formation chamber 7 b, HMDS and oxygen gas aresupplied as the raw material gas to form a dense SiO₂ film (barrierlayer). Incidentally, when there is no need to distinguish between thevacuum pumps 71 a and 71 b, between the plasma electrodes 72 a and 72 b,and between the raw material gas pipes 73 a and 73 b, they will becollectively referred to as the vacuum pumps 71, the plasma electrodes72, and the raw material gas pipes 73, respectively.

Here, the buffer layer is lower in density and higher in adhesion thanthe barrier layer, and the barrier layer, which is conversely higher indensity than the buffer layer, has a better barrier property.

With the thin-film formation device 1 configured as above, when thesubstrate 2 is first conveyed from the conveyor roll 3 to the conveyorroll 4, the substrate 2 passes through the first film formation chamber7 a, where a buffer layer is formed. The substrate 2 on which the bufferlayer has been formed then passes through the second film formationchamber 7 b, where a barrier layer is formed over the buffer layer. As aresult of continuing this conveyance from the conveyor roll 3 to theconveyor roll 4, most of the substrate 2 that had been wound onto thecore 31 of the conveyor roll 3 moves to the core 41 of the conveyor roll4, and a buffer layer and barrier layer are laminated over substantiallythe entire surface of the substrate 2, and then the rotation directionof the core 31 and the core 41 is then reversed, the conveyancedirection of the substrate 2 reverses, and the substrate 2 goes backthrough the second film formation chamber 7 b and the first filmformation chamber 7 a, so another buffer layer is laminated over thebarrier layer. After this, the conveyance direction of the substrate 2is again reversed to form another barrier layer on the buffer layer, andthin-films are formed in the two film formation chambers 7 whilereversing the conveyance direction of the substrate 2, thereby allowingtwo types of thin-film to be laminated alternately. This means that asealing film providing both good barrier property and good adhesion canbe formed on the substrate 2.

The operational flow of a method for forming a sealing film on thesubstrate 2 using the above-mentioned thin-film formation device 1 willnow be described through reference to FIG. 3.

First, a substrate 2 that has been wound onto the core 31 of theconveyor roll 3 is set in place, and the substrate 2 is placed on theouter peripheral face 51 of the main roll 5, and then connected to thecore 41 of the conveyor roll 4 (step S1). The main roll chamber 6 andthe vacuum pumps 61 and 71 of the film formation chambers 7 are thenactuated, and the insides of the film formation chambers 7 are broughtto the specified pressure (step S2). The pressure inside the first filmformation chamber 7 a here first becomes the pressure P1 necessary toform a buffer layer on the surface of the substrate 2 (film formationsurface). More specifically, this pressure P1 is about a few dozenpascals.

After the chambers have reached the specified pressure, raw material gasand discharge gas are supplied from the raw material gas pipes 73 of thefilm formation chambers 7 and from discharge gas pipes (not shown), andhigh-frequency voltage is applied to the plasma electrodes 72 by ahigh-frequency power supply (step S3). At this point the gas is suppliedand is then decomposed by the plasma, so that the pressure in the filmformation chambers 7 becomes higher than before the gas is supplied, andtherefore, in the above-mentioned step S2, this is taken into accountand the pressure is reduced in the film formation chambers 7 so that theinternal pressure of the film formation chambers 7 after gas supply willbe the pressure that is set for thin-film formation.

Next, the conveyor roll 3 and the conveyor roll 4 are driven to commencethe conveyance of the substrate 2 from the conveyor roll 3 toward theconveyor roll 4 (step S4).

The substrate 2 conveyed from the conveyor roll 3 toward the conveyorroll 4 first moves into the first film formation chamber 7 a. In thefirst film formation chamber 7 a, the raw material gas decomposed byexposure to the plasma atmosphere comes into contact with the substrate2, and a buffer layer is formed on the film formation surface of thesubstrate 2. That is, the substrate 2 touches the raw material gas whilebeing conveyed over the outer peripheral face 51 of the main roll 5, anda buffer layer is formed in the lengthwise direction on the filmformation surface of the substrate 2 (step S5). The buffer layer thusformed directly on the film formation surface of the substrate 2 iscalled the first buffer layer in the present invention, and the step offorming this first buffer layer is called the first buffer layerformation step in the present invention.

The substrate 2 that has passed through the first film formation chamber7 a then goes into the second film formation chamber 7 b. In the secondfilm formation chamber 7 b, the raw material gas that decomposed byexposure to the plasma atmosphere comes into contact with the substrate2, forming a barrier layer over the first buffer layer (step S6). Thebarrier layer thus formed on the surface of the first buffer layer iscalled the first barrier layer in the present invention, and the step offorming this first barrier layer is called the first barrier layerformation step in the present invention. After the first buffer layerand the first barrier layer have been laminated and formed on thesubstrate 2, the substrate 2 is wound onto the conveyor roll 4.

Then, after nearly all of the substrate 2 has been wound onto theconveyor roll 4, the pressure in the first film formation chamber 7 a,in which the buffer layer is formed, is further lowered to a pressure P2that is lower than the above-mentioned pressure P1 (step S7). Inspecific terms, this pressure P2 is about a few pascals. The method forlowering the pressure in the first film formation chamber 7 a may, forexample, be to change the aperture of a valve and thereby raise theamount of exhaust gas produced by the vacuum pump 71 a, or to reduce theamounts in which the raw material gas and the discharge-use gas aresupplied.

Next, the rotational direction of the conveyor roll 3 and the conveyorroll 4 is reversed, and the conveyance direction of the substrate 2 isreversed (step S8).

The substrate 2 that is conveyed from the conveyor roll 4 toward theconveyor roll 3 when the conveyance direction is reversed first passesthrough the second film formation chamber 7 b, which increases thethickness of the first barrier layer, after which the substrate 2 entersthe first film formation chamber 7 a, and a buffer layer is formed onthe surface of the first barrier layer under conditions in which thepressure in the chamber is P2 (step S9). The buffer layer thus formedover the first barrier layer is called the second buffer layer in thepresent invention, and the step of forming this second buffer layer iscalled the second buffer layer formation step in the present invention.

After this, barrier layers and buffer layers are formed while repeatedlyreversing the conveyance direction of the substrate 2, the result beingthat a sealing film in which the specified numbers of buffer layers andbarrier layers have been alternately formed is formed on the filmformation surface of the substrate 2 (step S10). Thus, a sealing filmproduced by alternately laminating buffer layers, which have betteradhesion than the barrier layers, and barrier layers, which have abetter barrier property than the buffer layers, combines the advantagesof both the buffer layers and the barrier layers, and therefore has bothgood barrier property and good adhesion. The pressure inside the firstfilm formation chamber 7 a after the second buffer layer formation stepis equal to the pressure P2 in the second buffer layer formation step,that is, it is lower than the pressure P1 in the first buffer layerformation step, and the pressure inside the second film formationchamber 7 b is kept constant (at the pressure in the first barrier layerformation step).

Finally, after the voltage applied to the plasma electrodes 72 drops tozero and the plasma is extinguished in the film formation chambers, theentire substrate 2 has been wound onto one of the conveyor rolls, andsaid conveyor roll is then removed from the thin-film formation device 1and the substrate 2 is sent to the next step (step S11).

Next, the structure of the sealing film obtained by the method forforming a sealing film pertaining to the present invention is shown inFIG. 4.

Buffer layers M1 and barrier layers M2 are alternately laminated on thesurface (the film formation surface) of the substrate 2 by means of theabove-mentioned sealing film formation method. Here, as discussed above,the pressure in the first film formation chamber 7 a in the first bufferlayer formation step of laminating the first buffer layer M1 a is higherthan the pressure in the first film formation chamber 7 a in the secondbuffer layer formation step of laminating the second buffer layer M1 b.Consequently, even though the two buffer layers are formed from the sameraw material, the film formation states are different. Morespecifically, even though the thickness A1 of the first buffer layer M1a is the same as the thickness A2 of the second buffer layer M1 b in thethickness direction of the substrate 2 indicated by an arrow in FIG. 4,the thickness B1 of the first buffer layer M1 a is greater than thethickness B2 of the second buffer layer M1 b in a direction that isinclined to the thickness direction of the substrate 2. That is, theratio of the thickness of the portion of the first buffer layer M1 aformed in the thickness direction of the substrate 2 relative to thethickness of the portion formed in a direction that is inclined to saidthickness direction, which is expressed by the quotient of dividing thethickness B1 by the thickness A1 (B1/A1), is closer to 1 than the ratioof the thickness of the portion of the second buffer layer M1 b formedin the thickness direction relative to the thickness of the portionformed in a direction that is inclined to this thickness direction,which is expressed by the quotient of dividing the thickness B2 by thethickness A2 (B2/A2).

Thus forming the films so that the thickness B1, thickness of the firstbuffer layer M1 a in a direction that is inclined to the thicknessdirection of the substrate 2, is made thicker allows the first bufferlayer M1 a to be formed in a sufficient thickness even on the surface ofthe stepped portion of the substrate 2. Consequently, the first bufferlayer M1 a is formed without any missing parts, so this avoids theproblem of the barrier layer that is subsequently formed not sticking.

One reason here for raising the pressure in the first film formationchamber 7 a to increase the thickness of the buffer layers M1 in adirection that is inclined to the thickness direction of the substrate 2would be to shorten the mean free path of the raw material gas byraising the pressure, which allows the raw material gas to easily reachnot only portions formed in the thickness direction of the substrate 2,but also portions that are inclined by about 90 degrees to the thicknessdirection, as shown in FIG. 4, for example. Also, when the pressurerises, the electron temperature drops and the reactivity of the rawmaterial gas becomes lower, so not only does much of the raw materialadhere to portions that are reached linearly from the direction of theplasma electrode 72 a, but also much of the raw material adheres toportions that are reached indirectly when the raw material bounces offthe surface of the thin-film, such as a portion that is inclined by 90degrees to the thickness direction.

However, with the discharge gas that is converted into a plasma underconditions of high pressure in the first film formation chamber 7 a, thedischarge gas molecules have less energy, so there is the risk thatundecomposed raw material gas will increase when the raw material gas isdecomposed in this low-energy plasma. If this happens, the undecomposedraw material gas will form a thin-film (buffer layer) in a state inwhich impurities remain in its interior, so the film density will belower, and as a result there is the risk of an inferior barrierproperty. Accordingly, it is undesirable for all of the buffer layer inthe sealing film to be in a state such as this.

Therefore, if film formation is carried out under conditions in whichthe pressure in the first film formation chamber 7 a is high only forthe first buffer layer M1 a, giving more importance to coverage (whetheror not the substrate 2 can be evenly covered), so that the film isformed by increasing the coverage at the expense of the barrierproperty, and the subsequent buffer layers M1 are formed underconditions in which the pressure in the first film formation chamber 7 ais lower, then a sealing film can be stably formed on the substrate 2with almost not decrease in the barrier property of the sealing film asa whole. Also, the sealing film will be less likely to become too thick.

Also, if the configuration is such that both the first buffer layer M1 aand any other buffer layers M1 are formed by varying the pressure in thefirst film formation chamber 7 a, it will be possible to form the entiresealing film within a single thin-film formation device, and compared towhen a sealing film is formed by replacing the substrate 2 in a numberof devices, particles are prevented from becoming stuck between thebuffer layers M1 and the barrier layers M2, and since both the firstbuffer layer M1 a and other buffer layers M1 can be formed from the sameraw material gas, the cost of the raw material gas used for sealing filmformation can be kept low.

The above method for forming a sealing film makes it possible to stablyform a sealing film having a good barrier property.

In the above description, all of the buffer layers M1 are formed in asingle first film formation chamber 7 a by reversing the conveyancedirection of the substrate 2, but it is also possible to dispose filmformation chambers for forming the buffer layers M1 and film formationchambers for forming the barrier layers M2 alternately and in series inthe conveyance direction of the substrate 2, and set the pressure injust the chamber for forming the first buffer layer M1 a higher than thepressure in the film formation chambers for forming the other bufferlayers.

Also, an example is given above in which film formation is performedusing plasma CVD, but thermal CVD, MOCVD, or another such vacuum filmformation method may be used instead of plasma CVD.

Also, if we focus only on the fact that the thickness of the bufferlayers M1 is increased in a direction that is inclined to the thicknessdirection of the substrate 2 for just the first buffer layer M1 a, thenthe formation of the first buffer layer M1 a may be performed in a stepother than plasma CVD, such as coating, and the lamination of thebarrier layers M2 and the buffer layers M1 may be performed subsequentlywith the thin-film formation device 1 discussed above.

Also, in the above description, two thin-films of the buffer layers M1and the barrier layers M2 are alternately laminated, but three or moretypes of thin-film may instead be formed in order.

1. A method for forming a sealing film, in which a buffer layer and abarrier layer whose density is higher than that of the buffer layer arealternately formed on a substrate, the method comprising: forming afirst buffer layer on a surface of the substrate; forming a firstbarrier layer on a surface of the first buffer layer; and forming asecond buffer layer on a surface of the first barrier layer, a ratio ofa thickness of a portion of the first buffer layer in a thicknessdirection of the substrate relative to a thickness of a portion of thefirst buffer layer in an inclined direction that is inclined withrespect to the thickness direction being closer to 1 than a ratio of athickness of a portion of the second buffer layer in the thicknessdirection relative to a thickness of a portion of the second bufferlayer in the inclined direction.
 2. The method for forming a sealingfilm according to claim 1, wherein the buffer layer and the barrierlayer are formed by CVD, and a film formation pressure applied duringthe forming of the first buffer layer is higher than a film formationpressure applied during the forming of the second buffer layer.
 3. Asealing film formed by alternately forming a buffer layer and a barrierlayer whose density is higher than that of the buffer layer on asubstrate, the sealing film comprising: a first buffer layer disposed ona surface of the substrate; a first barrier layer disposed on a surfaceof the first buffer layer; and a second buffer layer made of the sameraw material as the first buffer layer and disposed on a surface of thefirst barrier layer, a ratio of a thickness of a portion of the firstbuffer layer in a thickness direction of the substrate relative to athickness of a portion of the first buffer layer in an inclineddirection that is inclined with respect to the thickness direction beingcloser to 1 than a ratio of a thickness of a portion of the secondbuffer layer in the thickness direction relative to a thickness of aportion of the second buffer layer in the inclined direction.
 4. Thesealing film according to claim 3, wherein the first buffer layer hasdensity that is lower than that of the second buffer layer.
 5. Thesealing film according to claim 4, wherein the buffer layer and thebarrier layer are formed by CVD, and a film formation pressure appliedduring forming of the first buffer layer is higher than a film formationpressure applied during forming of the second buffer layer.
 6. Thesealing film according to claim 3, wherein the buffer layer and thebarrier layer are made of different raw materials.
 7. The method forforming a sealing film according to claim 1, wherein the first bufferlayer has density that is lower than that of the second buffer layer. 8.The method for forming a sealing film according to claim 1, wherein thefirst buffer layer and the second buffer layer are made of the same rawmaterial.
 9. The method for forming a sealing film according to claim 1,wherein the buffer layer and the barrier layer are made of different rawmaterials.